Conventionally, there has been known a flow rate measuring device that measures a parameter other than a flow rate of an intake air, such as a moisture, a temperature, or a pressure, in addition to the flow rate (see, e.g., Patent Literature 1: JP 2015-004556 A and Patent Literature 2: JP 2010-043883 A).
To generate detection signals for the parameter other than the flow rate, a sensor chip needs to be exposed to a flow of the intake air. Therefore, it is necessary to prevent such a sensor chip from being in contact with foreign substances or water drops included in the intake air.
Hereinafter, a sensor chip necessary to be exposed to a flow of the intake air for detecting a parameter is referred to as a “protection-required chip”.
There are following measures to protect the protection-required chip.
A first measure is that foreign substances and water drops are removed from an intake air using a linearly inertial force or a centrifugal force, and then the protection-required chip is exposed to the intake air after removing the foreign substances and the water drops.
A second measure is that the protection-required chip is covered by a filter in a state where the filter is away from the protection-required chip with a certain distance. In this measure, a frame body made of resin is required and the filter is fixed to the frame body by heat welding. A third measure is that the protection-required chip is covered by the filter by directly attaching the filter to the protection-required chip with an adhesive. Alternatively, the filter may be attached to a pre-molded component formed by resin-molding the protection-required chip.
However, in the first measure, it is necessary to provide a structure to remove foreign substances or water drops from an intake air, and a passage for the intake air after the foreign substances and the water drops are removed. As a result, the size of the device may become large. In the second measure, it is necessary to provide the resin made frame, whereby the size of the device may also become large. In the third measure, the adhesive may be denatured under a high temperature environment, and as a result, the filter is removed from the protection-required chip.
Therefore, a protection structure for the protection-required chip without the above-described defects existing in the three measures has been required.
In view of the above, it is an objective of the present disclosure to provide a flow rate measuring device that measures at least one of a flow rate of an intake air and a parameter other than the flow rate, where an increase in the size of the device and a concern that a filter is removed can be avoided.